Radiation-induced mixing and demixing behavior in metallic multilayers exhibiting limited solid miscibility

In this paper, radiation behavior of nanolayered zirconium/niobium and copper/niobium composites subjected to high irradiation doses will be discussed. The nanocomposites were synthesized in bulk form by accumulative roll bonding, a severe plastic deformation technique. Both systems show limited solubility at the irradiation temperature and exhibit a positive heat of mixing. The multilayers were subjected to self-ion irradiated doses of 140-200 dpa (displacements per atom) with Zr2+ and Cu2+ ions. Cross-sectional transmission electron microscopy examination indicates that zirconium/niobium multilayers with layer thicknesses spanning 15-80nm have undergone chemical mixing of layers and grain growth beneath the irradiated surface. On the other hand, all copper/niobium multilayers showed remarkable stability of layers and sharp interfaces up to 200 dpa dose, except for the thickening of copper and niobium layers in the maximum dose region. The observed mixing/demixing behavior in multilayers is attributed to chemically-driven interphase diffusion events within the thermal spikes. The experimental results validates that the chemical distribution under ion-radiation is sensitive to liquid-phase solubilities. The talk would emphasis the dependence of final microstructure and solute partition on the competition between migration of atom species triggered by the irradiation-induced thermal spikes and the thermally-activated radiation enhanced diffusion.